1. Field of the Invention
The present invention relates to an ink jet recording material and processes for producing the same. More particularly, the present invention relates to an ink jet recording material having excellent gloss and ink-absorption and capable of recording ink images with excellent color density, and processes for producing the same.
2. Description of the Related Art
The ink jet recording system is an ink image recording system wherein ink droplets are jetted through an ink-jetting nozzle toward a recording material at a high speed, and ink jetted droplets are absorbed in and fixed on the recording material, to form ink images. This ink jet recording system is advantageous in that full colored images can be easily formed and the printing noise is low.
The ink usable for the ink jet recording system contains a large amount of a solvent in which a coloring material is dissolved or dispersed and thus, to obtain a high color density of the recorded ink images, a large amount of the ink must be absorbed in the recording material. For the complete absorption of the ink droplets which have reached the recording material, a certain length of time is necessary. This feature of the ink jet recording system causes such a disadvantage that when the ink droplets are continuously jetted imagewise to form ink dots on the recording material surface, sometimes the ink droplets reach a target dot before an ink dot adjacent to the target dot has been completely absorbed in the recording material, and the target ink dot is connected to the adjacent ink dot so that the resultant ink image becomes unclear.
Accordingly if the recording material for the ink jet recording system is to have such an advantage that the ink dots formed thereon have high color density and brightness and a high clarity, the ink droplets must be rapidly absorbed therein and even if the ink dots are overlapped on each other, substantially no blotting of the ink may occur.
Currently, due to the rapid spread of ink jet printers, various ink jet prints with a high gloss are demanded for publications and packing paper sheets. Particularly, in colored prints, film type or coated sheet type ink jet recording sheets which have an appropriate dot form (true circle), a high dot sharpness, and high ink-receiving properties such as high ink-absorbing and fixing rates and a high ink absorption are in great demand.
To meet to the above-mentioned demands, a large number of types of ink jet recording sheets in which a coating layer containing an ink-absorbing pigment, for example, silica and alumina, and a binder is formed on a surface of a support sheet, are available. In these recording sheets, the pigments have the very small particle size of several xcexcm, and thus the surface of the resultant recording sheet is rough and a high gloss in the resultant prints is difficult to obtain. Also, since the coating layer is quite opaque, the applied ink is easily embedded in the coating layer and thus the color density of the resultant ink images is low. Namely, the droplets of ink easily spread between the fine pigment particles over a wide area and the color density in the image decreases with an increase in the distance from the center of the image. Also, the ink-spread area becomes unnecessarily large. Therefore, the color density of the ink image becomes low as a whole and the sharpness and clearness of the image decrease. Thus, undesirable unevenness and blotting of the image occur.
To solve the above-mentioned problems, Japanese Unexamined Patent Publication No. 62-111,782 proposed an ink jet recording material in which upper and under porous coating layers, different in porosity from each other, are formed on a support sheet, to control the ink-spread and to prevent unevenness and blotting of ink images. However, since the upper and under coating layers contain pigments having a relatively large particle size, in the xcexcm order, the resultant recording sheet was unsatisfactory in gloss and the color density of ink image.
Also, Japanese Unexamined Patent Publication No. 62-244,689 discloses an ink jet recording material in which a support is coated with an under coating layer containing a while pigment having a refraction of 1.50 or more and then with an upper coating layer containing a silicon pigment having a refraction of 1.43 to 1.48. This ink jet recording sheet can record ink images having a bright color and a high clarity. However, in this type of recording material, the pigments have a large particle size of 1 xcexcm or more, and thus the recording material exhibits an unsatisfactory gloss and the resultant ink images have an unsatisfactory color density.
Further, Japanese Unexamined Patent Publication No. 63-104,878 discloses an ink jet recording material in which a support is coated with a two-layered recording layer. In this recording layer, the pigments contained in an upper layer and a under layer are different in particle size, and one of the upper and under coating layers contains spherical silica particles, to enhance the ink-coloring property and the dot properties, for example, the true circle form of dots. However, the ink jet recording material is still unsatisfactory in gloss and color density of ink images.
For the purpose of enhancing the gloss of ink images and the ink-absorbing property of the ink jet recording material, currently, for example, Japanese Unexamined Patent Publication No. 7-101,142 and No. 7-117,335 disclose a two layered recording layer in which an upper coating layer serves as a high gloss-exhibiting layer. In these publications, since the high gloss-exhibiting layer contains primary particles of a pigment, the porosity of the high gloss-exhibiting layer is very low. Therefore, the high gloss-exhibiting layer has very small or substantially no space for receiving and fixing the ink, and thus can serve only as an ink-passing layer. Almost all of the applied ink can be fixed only in the coating layer. The under coat layer contains pigment particles having a particle size of a xcexcm order. Thus, the resultant under coating layer has a poor transparency, and thus cannot record ink images having a high color density. Therefore, this type of ink jet recording material substantially cannot record photographic image-like ink images having a high gloss and color density.
Further, EP-A-803374 discloses an ink jet recording material in which a support is coated with an ink receiving layer containing secondary particles having an average secondary particle size of 10 to 300 nm and consisting of primary particles having an average particle size of 3 to 40 nm and agglomerated with each other. This ink jet recording material can record photographic image-like ink images having a high gloss and a high color density. However, in the current ink jet printers, since the printing speed and ink-jetting rate are greatly increased, the blotting and unevenness of the printed ink images must be further prevented.
An object of the present invention is to provide an ink jet recording material having a high gloss, a high ink-absorbing property and a high resistance to blotting of ink and capable of recording clear ink images having excellent color density and sharpness, and processes for producing the same.
The above-mentioned object can be attained by the ink jet recording material of the present invention, which comprises a support and a multi-layered ink receiving layer comprising at least one under recording layer formed on the support and at least one upperrecording layer formed on the underrecording layer, wherein the under and upperrecording layers comprise secondary particles of a pigment having an average secondary particle size of 10 to 400 nm and each consisting essentially of a plurality of primary particles agglomerated with each other and having an average primary particle size of 3 to 40 nm, and the average primary particle size of the primary particles in the underrecording layer is larger than the average primary particle size of the primary particles in the upperrecording layer.
In a process of the present invention for producing an ink jet recording material comprising a support and a multi-layered ink receiving layer comprising at least one underrecording layer formed on the support and at least one upperrecording layer formed on the underrecording layer, the under and upperrecording layers comprising secondary particles of a pigment having an average secondary particle size of 10 to 400 nm and each consisting essentially of a plurality of primary particles agglomerated with each other and having an average primary particle size of 3 to 40 nm, and the average primary particle size of the primary particles in the underrecording layer is larger than the average primary particle size of the primary particles in the upperrecording layer,
at least one first coating layer corresponding to the at least one upperrecording layer is formed on a casting surface;
separately at least one second coating layer corresponding to the at least one underrecording layer is formed on a surface of a support;
the second coating layer-coated support is laminated on the first coating layer formed on the casting surface in such a manner that the surface of the second coating layer is brought into contact with and bonded to the surface of the first coating layer; and the resultant laminate is separated from the casting surface.
In another process of the present invention for producing an ink jet recording material comprising a support and a multi-layered ink receiving layer comprising at least one underrecording layer formed on the support and at least one upperrecording layer formed on the underrecording layer, the under and upper-recording layers comprising secondary particles of a pigment having an average secondary particle size of 10 to 400 nm and each consisting essentially of a plurality of primary particles agglomerated with each other and having an average primary particle size of 3 to 40 nm, and the average primary particle size of the primary particles in the underrecording layer is larger than the average primary particle size of the primary particles in the upperrecording layer, at least one first coating layer corresponding to the at least one upperrecording layer is formed on a casting surface;
at least one second coating layer corresponding to the at least one underrecording layer is formed on the first coating layer;
a support is laminated on the first and second coating layers on the casting surface; and the resultant laminate is separated from the casting surface.
Still another process of the present invention for producing an ink jet recording material comprises:
forming at least one dried coating layer comprising a binder and secondary particles of a pigment having an average secondary particle size of 10 to 400 nm and each consisting essentially of a plurality of primary particles agglomerated with each other and having an average primary particle size of 3 to 40 nm on a casting surface;
separately forming at least one coating layer comprising a binder and secondary particles of a pigment having an average secondary particle size of 10 to 400 nm and each consisting essentially of a plurality of primary particles agglomerated with each other and having an average primary particle size of 3 to 40 nm and larger than the average primary particles size of the primary particles in the dried coating layer formed on the casting surface, on a surface of a support;
laminating, while the surface of the coating layer formed on the support is kept in a wetted condition, the coating layer-coated support on the dried coating layer formed on the casting surface, in such a manner that the wetted coating layer surface on the support is brought into contact with and bonded to the dried coating layer on the casting surface; and
separating the resultant laminate from the casting surface.